Introduction

In South Australia, the Tall Yellow-top (Senecio pilosicristus) is a rare daisy which was historically collected in the Karoonda to Lameroo area in the Murraylands region of the state. The majority of herbarium collections for c were from the 1910s to the 1960s. Apart from a single herbarium collection from an unknown locality in 1984 there have been no further herbarium collections in SA. This species also occurs in western Victoria where it is considered very rare and it is currently listed as vulnerable in Victoria. There is little is known about the biology and habitat of the Tall Yellow-top.

The South Australian Seed Conservation Centre (SASCC), based at the Adelaide Botanic Gardens, is dedicated to the conservation of the state’s threatened native plants. More specifically this includes locating plants and recording habitat details, collecting and banking seeds, research to determine germination requirements and the propagation of plants to assist with restoration programs. Staff at the SASCC identified the Tall Yellow-top as a priority species to locate and collect seeds. The historic location information and lack of recent records suggested that this species may occur on the more fertile loams that have since been cleared for cropping. Although there were no notes with herbarium vouchers to suggest that the Tall Yellow-top was collected post fire, it was suspected that the lack of records may indicate this species might only be detectable after environmental disturbance events such as bushfire.

Field searches

In recent years, staff from the SASCC have searched some of the historical South Australian localities for the Tall Yellow-top without success. The majority of the land where historic records were made has been substantially cleared for agricultural use and the fragmented remnant vegetation is highly impacted by numerous introduced plants and animals.

However in September 2010, a chance find of a post burn site in Billiat Conservation Park (CP) during field searches yielded success. A small population of the Tall Yellow-top was located in a mallee woodland fire scar growing in a low open swale on pale red sandy loams in regenerating mallee with other specific fire responsive species such as Small-leaf Ray Flower (Cyphanthera myosotidea), False Buckbush (Gyrostemon australasicus), Azure Daisy-bush (Olearia rudis), Branched Everlasting (Coronidium adenophorum), Oondooroo (Solanum simile), Cup Velleia (Velleia connata), Twiggy Lignum (Muehlenbeckia diclina) and Williamson’s Riceflower (Pimelea williamsonii). This localised population contained at least a few hundred individuals. Apart from a sub-population of approximately fifty plants that was identified another 800 m north of the original population, no further populations have been recorded during follow up searches within a radius of 7 km. Photos of the characteristics of the plant such as flower, leaves and habit were taken along with pressed plant specimens in order to build knowledge about this daisy.

Regional staff working for the Department of Environment and Natural Resources (DENR) based in the area were made aware of this population and asked to monitor other post-fire mallee in the region for this species. A follow up visit to the population twelve months later (spring 2011) revealed a small number of plants resprouting. However these plants produced much less vigorous growth than observed during the previous spring immediately post fire. This observation suggests that although plants can persist for a second year post-fire, this species is quite short‑lived.

Observations of the plant characteristics

The Tall Yellow-top is an erect, fleshy, glaucous, short-lived herb to approximately 70 cm tall. It has sessile, stem clasping, tapered-lanceolate cauline leaves on reddish purple stems with a basal rosette of lobed spathulate leaves. Flowers are a yellow daisy up to 50 mm in diameter with up to ten ray petals. The seeds are a brown achene with longitudinal ridges of white hairs and white pappus.

Germination research

The SASCC collected and banked more than eight thousand seeds for this rare daisy in 2010 and has undertaken research to determine its germination requirements. Germination screening was undertaken for this species in both winter and spring diurnal conditions using gibberellic acid, potassium nitrate and untreated controls. Gibberellic acid is a naturally occurring plant growth hormone which can alleviate seed dormancy in some species. Potassium nitrate was used because the availability of free nitrogen post fire as nitrates in the soil can act as a ‘gap detection’ signal and provide a cue for seed germination. No germination was recorded for the untreated controls or the seeds which received potassium nitrate treatment in either winter or spring conditions. Whilst only a single germinant resulted from gibberellic acid treatment in spring conditions, a germination rate of 42% was achieved with gibberellic acid in winter conditions. These results suggest the Tall Yellow-top specifically prefers winter conditions for germination. Further research is required to ascertain the germination response to environmental cues such as heat and smoke chemicals.

The future

Staff at the SASCC anticipate that more populations of the Tall Yellow-top will be observed in post fire mallee in the region. The DENR regional ecologist working in the Murray region has identified and mapped further areas of mallee for prescribed burning which may be potential habitat for the Tall Yellow-top. Regional staff and the SASCC will perform further searches in spring 2012 upon completion of prescribed burns for Billiat CP scheduled for autumn 2012. In addition to the Tall Yellow-top, this will be an opportunity for regional and SASCC staff to monitor for other fire responsive species such as the nationally vulnerable Yellow Swainson-pea (Swainsona pyrophila) and Showy Lawrencia (Lawrencia berthae) which is listed as rare in South Australia and vulnerable in Victoria.

Field observations of the Tall Yellow-top and the collation of valuable information about the biology and habitat of this daisy have been shared with interested parties, including the DENR regional ecologist. This will increase the chances of finding additional populations. Future germination experiments utilising fire related treatments such as heat and smoke may provide an opportunity to understand environmental germination cues and techniques for growing plants for regional restoration projects.

Acknowledgements

We would like to acknowledge the support of the Native Vegetation Council which has enabled the SASCC to perform project work in the Murray region. We would also like to acknowledge the assistance of Thai Te, Jenny Guerin, Ellen Ryan-Colton and Denzel Murfet during field searches and laboratory work.